>I think the algebra functions and where
clauses work well as a filtering system when objects
>datatypes are similar to that of a RDBMS,
that is numerical and alphanumerical values. However,
>complex datatypes in objects require at times
more sophisticated form of query. For example a
>vector model or a 3D polygon model in form of
a object has little use of the operators mentioned.
One of the key features of OO is that you define the operations on your
datatypes, much as in SQL the greater-than function is predefined on numbers,
the boolean function like( regexp) is defined on strings etc. For OO I speak
of filters whose functions are not statically defined, but dynamic, since
objects carry both data and method. If a polygon defines the method
inFrontOf(), you are able to use that in the query.
Complex objects doesn't increase complexity in the queries. They just
demand another set of boolean operations. In the old RDBMS world, the
operations were predefined since the datatypes were predefined. In OO systems,
one is able to create datatypes dynamically. From that follows that one has to
be able to define the operations too.
Anyhow, all this is meaningless to discuss now, since the pioneers in OO
had all these thoughts years ago. Let's continue the OO-query discussion from
today's point of view.
My mention of algebra referred solely to set algebra. SQL's SELECT deales
only with set algebra (every SELECT statement defines a subset from a larger
set), and OO queries must be able to do this as well.
>In trying to replicate SQL that is then 10 years old is
reverting to ancient and old technology.
Well, I don't think you got me right. SQL might be outdated, but what you
need to do with data sets remains the same, as well as what you are able to do
with them. It is way too early to speak about front-ends. [ In fact, thinking
of core functionality and methods to control it (GUI or whatever) as a
conceptual unit is in itself pretty outdated. I am sure we all can come up
with excellent methods to access the data, as soon as we have a good language
(in the mathematical sense of the word) for it].
BTW: can anyone recommend a book or a paper on where OO database science
is right now? The OO discussion has been centered alot around patterns and
modelling techniques the last years. What's happening out there?
/O